Existing ventilation systems for buildings that are integrated with forced air heating, ventilation, and/or air conditioning (HVAC) systems have one or more deficiencies. These may include the introduction of cold outside air to the furnace or HVAC device, creating the potential for excessive condensate, a cracked heat exchanger, or other conditions that lead to system failure. Existing systems are not typically able to accommodate more than one return air duct, while many of today's HVAC systems require two or more return air ducts.
Existing integrated ventilation systems utilize the blower of the furnace/HVAC device to draw in outside air and supply it to the conditioned space, typically necessitating modification of the furnace/HVAC device controls to accommodate this supplementary usage of the blower. Otherwise, if a second controller is employed, the blower could receive conflicting signals output from the two controllers, which could cause the blower and/or furnace/HVAC device to malfunction, operate incorrectly, or become disabled. The design of furnace/HVAC device controls varies by brand and model, thus necessitating a large number of varying controls modifications to enable the integration of a ventilation system with multiple furnace/HVAC device brands and models. This can add significant development, manufacturing and logistical costs to the provision of integrated ventilation systems, limiting market penetration and perpetuating poor indoor air quality and high cooling energy use in buildings. In addition, existing integrated ventilation systems typically require use of a custom thermostat. This also can limit usage, as many users already own or prefer one of the many commonly available thermostats.